As the polymer latex (or emulsion) usable as an additive to the paper stock in papermaking, an anionic substance is generally known. In this case, it is necessary that the polymer latex be employed along with aluminum sulfate or a cationic water-soluble polymer whereby the latex grains are coagulated and coarsened to be well fixed to the paper stock.
Japanese Patent Application Laid-Open No. 61-261302 mentions cationic polymer latexes.
As opposed to this, the applicant's Japanese Patent Application No. 62-304460 mentions a polymer latex of composite structure having amphoteric ions as distributed very densely on the surfaces of the emulsion grains.
The polymer latex to be employed as an additive to a paper stock is required to have higher fixability and also have higher bindability and adhesiveness to fibers or a filler, because of the economics.
The latex to be employed in the method of the present invention has amphoteric ions at the same time and displays a cationic property on the average. Accordingly, it not only has a function of adsorbing to fibers or a filler but also an interaction between the latex grains themselves. Therefore, has an excellent self-fixability even though it is not combined with an additional fixing agent such as aluminum sulfate or a cationic water-soluble polymer.